Method of and apparatus for producing semiconductor material



March 3, 1959 H. KNIEPKAMP ET AL ,876,

METHOD OF AND APPARATUS FOR PRODUCING SEMICONDUCTOR MATERIAL Filed May21, 1956 2 Sheets-Sheet 1 March 3, 1959 H. KNIEPKAMP ET AL 2,876,147

METHOD OF AND APPARATUS FOR pnonucmc SEMICONDUCTOR MATERIAL Filed14:13:21, 1956 2 Sheets-Sheet 2 United States Patent METHOD OF ANDAPPARATUS FOR PRODUCING SEMICONDUCTOR MATERIAL Heinrich Kniepkamp andGiinther Ziegler, Karlsruhe,

Germany, assignors to Siemens & Halslre Aktiengesellschaft, Berlin andMunich, Germany, a corporation of Germany This invention is concernedwith a method of and apparatus for producing semiconductor material bydrawing rodlike bodies from a melt and applyingzone melting to saidbodies, all in one workingoperation.

Copending application of Karl Siebertz Serial No. 409,420 filed February10, 1954, having a common assignee, which describes a method of andapparatus for successively melting and solidifying semiconductormaterial in zones, applied primarily for purification purposes to anelongated preferably rodlike substantially perpendicularly disposed bodyfia'stened at its opposite ends, the melting zone being so small that itis supported by the adjacent solidified portions by adhering thereto.The advantage of the procedure is that it does not require a crucible,thereby avoiding contaminations which would otherwise result from thecrucible material. The disadvantagewith the rod fastened at its ends--isthat only one melting zone can be processed at any time. The procedureis, as compared with zone melting in a crucible, time consuming becauseit must be repeatedly applied while zone melting by means of a crucible,for example, a carbon well permits simultaneous processing of severalmelting zones. The simultaneous processing of several melting zones isin principle also possible with the rodlike body perpendicularly held atits ends provided that the rod is additionally supported at intermediatepoints, but these additional supports must be removed at the instant ofpassage of the melting zones through the corresponding regions.

The thought underlying the invention resides in recognition of the factthat the purification according to the zone melting process is the moreeffective the more the structure of the body to be purified approachesthat of a monocrystal, the purification being most effective in the caseof an ideal monocrystal.

The invention utilizes this fact by applying the zone melting describedin the previously mentioned copending application directly andimmediately upon drawing of crystals, especially monocrystals, from acrucible, thus combining the zone melting with the drawing in oneworking operation. The invention thereby contemplates to support thecrystal, preferably a monocrystal, drawn from the crucible, at twowidely separated points and to subject intervening areas to the zonemelting. The operation according to the invention results not only inthe advantage already mentioned, of accelerating the purification by thezone melting, but, in a particular embodiment, in giving the possibilityto operate the zone melting in a continuous process. The supportingpoints are thereby to be altered, steadily or abruptly, in accordancewith the length of the crystal drawn from the crucible. The speed atwhich the melting zone is drawn is to be matched to a certain extentwith the speed at which the crystal is drawn from the crucible. However,inasmuch as the speed of drawing depends in part on the thickness of therod, it will in some cases be necessary or suitable to interrupt or toslow down the crystal drawing at least Patented Mar. 3, 1959 for someintervals until the melting zones have been drawn once or several timesthrough a predetermined portion of the rod-shaped crystal.

The. foregoing and other objects and features of the invention willappear from the description which is rendered below with reference tothe accompanying schematic drawings, wherein- Fig. 1 shows an embodimentfor drawing a crystal rod from a crucible in upward direction; and

Fig. 2 illustrates an embodiment for effecting the drawing of a crystalrod in downward direction.

Referring now to Fig. l, numeral 1 indicates a crucible made for exampleof graphite, containing molten silicon or germanium 21. The crucible 1is provided with an extension 2 which is separately heated by means of acoil 3. The crystal 4 is in known manner drawn from the extension 2 inthe direction of the arrow 5. Rollers 15 and 16 movably journalled in abearing 7 are provided to support the upper end of the crystal 4.Numeral 8 indicates a belt extending from a drive roller 9 for rotatingthe rollers 15 and 16 to rotate the crystal rod 4 in the direction ofthe arrow 10. The crystal drawing is otherwise effected in known manner.

In accordance with the invention, there is provided a heating device 11,formed as an annulus, adapted to melt a narrow zone of the crystal rod4. This heating device 11 may be disposed within a casing 26 providedwith arms 27 carrying worm wheels 28 meshing with a worm 29, and may bedisplaced, for example, downwardly, in the direction of the arrow 12, byrotating the worm 29 in the direction of the arrow. The consequentlyproduced melting zone 13 is thereby drawn downwardly along thesolidified portion of the drawn monocrystal, effecting purification, andcontaminations are deposited at the lower end engaging the flaring mouth14 of the extension 2. The process is likewise employed in Fig. 2 thoughby opposite movement.

The pair of rollers 15-16 also serve for moving the crystal rod 4upwardly. There is provided, for this purpose, a ratchet 17 supported onan annular carrier 18 which may be displaced downwardly, by suitable notillustrated means, to rotate a gear wheel 19 for correspondinglyrotating the rollers 16 through the medium of a link 20, therebyadvancing the crystal rod 4 upwardly.

The operation is as follows:

The heating coil 3 is in suitable manner connected to a current source,heating the neck of the extension 2. The crystal rod 4 is now drawn fromthe crucible 1 in known manner. The drawing operation is thereuponinterrupted and the heating coil 3 is at the same time disconnected. Aportion of the melt within the extension 2, at least within the flaringmouth 14, accordingly solidifies. The crystal rod 4 is thus fixedlysupported at the bottom while being held at the top by the roller pairs15-16. The heating coil 11 is thereupon moved from the upper enddownward to the flaring mouth 14 of the extension 2, the melting zone 13moving along the rod 4. This operation may be repeated, if desired. Uponconclusion of the zone melting, the heating coil is again connected tocurrent. As soon as the material in the extension 2 and at least in partof the flaring mouth 14 has melted, the crystal drawing is continued,followed by zone melting, etc.

Upon remelting the material contained in the flaring mouth 14 of theextension 2, the contaminations collected therein, extracted in the zonemelting, will enter into the melt 21 in the crucible 1, resulting incontinually enriching the melt with contamination products. This effectis in part counteracted by continuously delivering to the melt 21purified semiconductor material 23 from the supply receptacle 22, suchdelivery being automat- 3 ically efiected by means of a float 24controlling a valve 25 disposed at the bottom of the receptacle 22. Ifdesired, the contaminated melt may be drawn off at another point of thecrucible, shown broken away at the right side, before delivering the newmelt material.

It is in this manner possible to draw in a continuous process crystalrods 4 of desired length and uniform purity as well as crystallinestructure. Portions of the crystal rod produced may be cut off at theupper end as desired or required.

The embodiment described above may be modified in several ways. Thus,several supporting means corresponding to the pairs of rollers 1516 maybe provided, and several melting zones such as 13 may be arranged forsimultaneous drawing relative -to the crystal rod. The heating coil 3may under some circumstances be omitted and its function may be etfectedby the heating coil 11. Additional supporting elements may be disposedat the lower end, and means may be provided for moving all supportingelements in the direction of drawing for the purpose of effecting acontinuous drawing operation while simultaneously applying the zonemelting.

Fig. 2 shows a modification in which the semiconductor crystal, ifdesired a monocrystal, is drawn downwardly from a melt 41 contained in acrucible 31. Rods are continuously drawn downwardly from the extensions32 and 33. These rods may be supported at their ends by meanscorresponding to the elements described in connection with Fig. 1. videdtapering extensions 34 and 35. The functions of the pairs of rollers 36and 37 shown in Fig. 2 correspond to those of the rollers 15-16 of Fig.l. The melting zones produced by the heating coils 38 and 39 are movedrelative to the two rods, by suitable not illustrated means,'in oppositedirections as indicated by arrows 40 and 41'. Contaminations are in thismanner respectively transported to the lower end of the left handcrystal rod and to the upper end of the right hand rod. The right handcrystal rod is produced for further processing, while the left hand rodserves for regaining melt material which is delivered to the crucible 31along the-path 42. The apparatus is encased in a housing 43 containing asuitable protective gas, preferably under pressure, to avoid droppingotf of melt at'the openings of the extensions 34 and 35. Numeral 44-indicates a manometer and 45 and 46 are locks or gates for theprotective gas flowing-in the direction of the arrow 47 to preventingress of air into the housing 43.

The arrangement according to Fig. 1 may be modified to provide for dualrod operation by employing features analogous to those incorporated inFig. 2.

Changes may be made within the scope and spirit the appended claims.

We claim:

1. A method of producing elongated generally rodshaped semi-conductorcrystal bodies, comprising'drawing a crystal body from a melt containedin a crucible while supporting said drawn crystal body at its ends, oneend of said crystal body being in operative contact relation with themelt while subjecting said one end to heating, subjecting anintermediate area of said crystal body immediately upon conclusion ofthe drawing thereof to zone melting, andmoving relative to said cruciblethe consequently produced melting zone along the solidified portion ofthe drawn crystal, elfecting purification and causing deposit ofcontaminations at the end of said crystal body in contact with the melt.

2. A method according to claim 1, comprisingcontinuously delivering meltmaterial to said crucible.

, 3. A method according to claim 1, comprising alternately drawing andzone melting said crystal body.

In the present case, there are pro 4. A method according to claim 1,comprising continuously drawing said crystal body and continuously zonemelting portions of said drawn crystal body at a speed adapted to thespeed of drawing.

5. A method according to claim 1, comprising drawing said crystal bodyfrom said crucible in upward direction.

6. A method according to claim 1, comprising drawing said crystal bodyfrom said crucible in downward dircction.

7. A method according to claim 5, comprising heating said crystal bodyduring said drawing at a point adjacent the melt in said crucible, saidcrystal body solidifying at said point so that the solidified body issupported adjacent the melt during the subsequent zone melting thereof.

8. A method according to claim 6, comprising heating said crystal bodyduring said drawing at a point adjacent I the melt in said crucible,said crystal body solidifying at said point so that the solidified bodyis supported adjacent the melt during the subsequent zone meltingthereof.

9. Apparatus for producing semiconductor crystal bodies, comprising acrucible adapted to contain molten semiconductor material, afunnel-shaped extension projecting upwardly from said crucible, meansfor vertically upwardly drawing an elongated generally rodlike crystalbody from said melt contained in said crucible, means for heating thematerial in said extension during drawing of said crystal body, thematerial in said extension par tially solidifying to serve as a supportfor said drawn crystal body at the lower end thereof with such lower endin operative contact relation with the melt in said crucible, means forsupporti g the drawn crystal body at the upper end thereof, andvertically movable heating means concentric with said rodlike crystalbodyand intermediate the ends of said body for subjecting said body tozone melting immediately after the drawing thereof from said melt.

10. Apparatus for producing semi-conductor crystal bodies, comprising acrucible containing molten semiconductor material, means for verticallydrawing anelongated generally rodlike crystal body from said meltcontained in said crucible, guide rollers in engagement with said drawncrystal body, said guide rollers forming part of said drawing means,means for rotating said guide rollers about the axis of said crystalbody to rotate such body, means for positively rotating a predeterminedguide roller to move said crystal body relative to said melt with oneend of said body in operative contact relation with said melt, heatingmeans comprising a heating coil concentric with the rodlike crystal bodyand intermediate the ends thereof for subjecting said crystal body tozone melting immediately after concluding the draw ing of said body fromsaid melt, and means for moving said heating means longitudinaly of saidcrystal body.

References Cited in the file of this patent UNITED STATES PATENTS2,553,921 Jordan May 22, 1951 2,623,253 Harrison Dec. 30, 1952 2,631,356Sparks et al. Mar 17, 1953 2,739,088 Pfann Mar. 20, 1956 2,743,200Hannay Apr. 24, 1956 2,768,914 Buehler ct al. Oct. 30, 1956 2,770,022Brennan Nov. 13, 1956 FOREIGN PATENTS 804,840 Germany Apr. 30, 19511,087,946 France Sept. 1, 1954

1. A METHOD OF PRODUCING ELONGATED GENERALLY RODSHAPED SEMI-CONDUCTORCRYSTAL BODIES, COMPRISING DRAWING A CRYSTAL BODY FROM A MELT CONTAINEDIN A CRUCIBLE WHILE SUPPORTING SAID DRAWN CRYSTAL BODY AT ITS ENDS, ONEEND OF SAID CRYSTAL BODY BEING IN OPERATIVE CONTACT RELATION WITH THEMELT WHILE SUBJECTING SAID ONE END TO HEATING, SUBJECTING ANINTERMEDIATE AREA OF SAID CRYSTAL BODY IMMEDIATELY UPON CONCLUSION OFTHE DRAWING THEREOF TO ZONE MELTING, AND MOVING RELATIVE TO SAIDCRUCIBLE THE CONSEQUENTLY PRODUCED MELTING ZONE ALONG THE SOLIDFIEDPORTION OF THE DRAWN CRYSTAL, EFFECTING PURIFICATION AND CAUSING DEPOSITOF CONTAMINATIONS AT THE END OF SAID CRYSTAL BODY IN CONTACT WITH THEMELT.